Field experiments were conducted to quantify cumulative and annual rates of woolly cupgrass seedling emergence and seed mortality and to characterize woolly cupgrass seedling emergence patterns. Woolly cupgrass seed bank decline was rapid, declining by an average of 73, 96, and 99.5% after 1, 2, and 3 yr, respectively. Woolly cupgrass seed mortality accounted for a much greater portion of seed loss from the seed bank (80%) than germination and emergence (19.5%) during the 3-yr period. Annual rates of emergence ranged from 3 to 17% of the fall seed bank and were similar between seed banks established in different years when compared within the same year. Annual rates of mortality ranged from 50 to 92% and varied between seed banks established in different years when compared within the same year; older seed banks had higher rates of mortality than younger seed banks. For first-year seed banks, 97 to 99% of the total season emergence occurred within the first 3 wk of emergence. However, for second- and third-year seed banks, a greater percentage of the total season emergence occurred later in the season compared with emergence that occurred during the first year. The data suggest that in addition to various environmental and seed-source factors, seed bank age may also play a role in seed mortality rate and seedling emergence pattern.

Field experiments were established in fall 1999 and 2000 near Huntley, MT, to determine the effects of soil water content on wild oat seed mortality and seedling emergence. Four supplemental irrigation treatments were implemented from June through September to establish plots with varying soil water content. Wild oat seed mortality during the summer increased linearly as soil water content increased. For seed banks established in 1999 (1999SB), seed mortality increased, on average, from 36 to 55% in 2000, and 15 to 55% in 2001 as soil water content increased from 6 to 24%. For seed banks established in 2000 (2000SB), seed mortality increased, on average, from 38 to 88% in 2001 and 53 to 79% in 2002 as soil water content increased from 6 to 24%. Increasing soil water content likely increased the activity of microorganisms that cause mortality in wild oat seeds. The increasing seed mortality rates (due to increasing soil water content) resulted in greater annual declines of wild oat seed banks and 2-yr cumulative decline rates. Total season emergence percentage was not affected by irrigation treatment. Results show that weed seed bank decline is more rapid in moist than in dry soils and suggest that management practices that increase or conserve soil moisture will also increase the rate of wild oat seed bank decline.